The Department of Transportation levied a total of $14.3 million in penalties for violations of air travel consumer-protection rules over the past ten years (read “Activist DOT collects $3.6 million for airlines’ consumer-protection violations in 2012” for more background). Violations were imposed 210 times on legacy, regional, low-cost airlines from the U.S. and abroad, and 58 of these went to major U.S. airlines. An additional 55 violations were issued to travel agencies and tour operators. U.S. Airways was at fault for six of those violations, while American Airlines took responsibility for two.

American’s troubles stemmed from on-the-ground operation errors, while US Airway’s oversights were largely on the backend leading to website and reservation snafus.

This will be the second airline merger to occur since the Department of Transportation took a more activist role and enacted two new consumer-protection rules in 2010 and 2011. The carriers will have to attempt to stay within the regulations’ boundaries while working out the kinks of their merger.

As a primer of what’s to come, we looked at the DOT violations of each airline over the past decade.

US Airways muddles online sales

US Airways thrice violated US Code – Section 41712, which prohibits carriers and ticket agents from engaging in an “unfair or deceptive practice or an unfair method of competition in air transportation or the sale of air transportation.”

The airline was fined a total of $185,000 for online pricing violations in 2008, 2010, and 2011. It’s worth noting that companies fined by the DOT generally only have to pay half the fine if they comply with their consent agreements for one year.

The three fines are as follows:

June 2011 – $45,000: US Airways was fined for not prominently displaying, either through a link or asterisk, the additional taxes and fees that consumers would have to pay in an airfare promotion to Rome.

March 2010 – $40,000: US Airways failed to display, or even mention, additional taxes and fees that would apply to airfares displayed after consumer initiated a search for one-way airfares. US Airways said the mistake was unintentional and a programming mistake.

Febuary 2008 – $100,000: US Airway’s website did not clearly or completely disclose the fee for lap infants — 10 percent of the total airfare plus taxes paid by an adult — which misled a number of passengers to believe that infants flew for free.

US Airways said the infant fee confusions stemmed from the American West merger and problems that resulted in the process of integrating the information of the two websites onto a single platform.

It’s likely that consumers will come across similar bumps in the integration of the US Airways and American Airlines’ websites, although travelers won’t see any changes to the sites for months after a potential merger is announced.

Inconsistent customer service

US Airways was fined three other times in the past decade for failing to disclose codeshares, failing ask for volunteers before bumping fliers from flights, and failing to provide on-time performance numbers to consumers.

August 2009 – $70,000: Reservations agents neglected to mention the status of US Airways codeshare flights, which are operated by outside carriers, on a substantial number of calls with customers.

December 2008 – $140,000: It was fined again for a series of mistakes made when bumping passengers from flights. The airline failed to first ask for volunteers to leave flights, it neglected to provide passengers with a written statement of their options or compensation in a timely matter after being involuntarily bumped.

April 2008 – $50,000: Reservation agents failed to provide on-time performance information to consumers when asked on the phone. The reservation agents said they didn’t have the on-performance information or were unfamiliar with its availability.

American’s two fines in 2011

In comparison, American Airlines and its subsidiary American Eagle have been charged once each in the past decade. AA was charged in February 2011 for $90,000 for failing to disclose the amount of fees and use restrictions on travel vouchers given to passengers who volunteered to give up their seats in oversales situations.

American Eagle was later fined $900,000 in November 2011 for holding a total of 608 passengers across 15 flights for more than three hours on the tarmac on a particularly foggy day at Chicago O’Hare Airport. Passengers were held anywhere from 3 to 45 minutes over the 3-hour mark.